Special fibers are a class of optical fibers that are designed for specific applications that require unique optical, mechanical, or environmental properties. Special fibers can be divided into two broad categories: single-mode fibers and multi-mode fibers.
Single-mode special fibers are typically designed for applications that require very low signal attenuation and high bandwidth, such as long-haul telecommunications, high-speed data transmission, and optical sensing. Single-mode fibers can be further divided into several sub-categories:
Polarization-maintaining fibers: These fibers are designed to maintain the polarization state of light, which is important in certain applications such as interferometry, fiber optic gyroscopes, and polarization-sensitive sensors.
Dispersion-shifted fibers: These fibers are designed to reduce the effects of chromatic dispersion, which can limit the transmission distance and bandwidth of fiber optic systems. Dispersion-shifted fibers are typically used in long-haul telecommunications systems.
Non-zero dispersion-shifted fibers: These fibers are designed to have a small amount of chromatic dispersion, which can help to improve the transmission distance and bandwidth of fiber optic systems. Non-zero dispersion-shifted fibers are typically used in high-speed data transmission and high-power fiber lasers.
Photosensitive fibers: These fibers are designed to change their refractive index when exposed to light, which can be useful for applications such as fiber Bragg gratings, optical switches, and sensors.
Multi-mode special fibers are typically designed for applications that require large core diameters, high numerical apertures, and/or high damage thresholds, such as laser delivery, fiber optic sensing, and medical applications. Multi-mode fibers can be further divided into several sub-categories:
Large-core fibers: These fibers have core diameters of several hundred microns or more, which can help to reduce the effects of modal dispersion and improve coupling efficiency. Large-core fibers are typically used in laser delivery and fiber optic sensing applications.
Graded-index fibers: These fibers have a graded refractive index profile, which can help to reduce the effects of modal dispersion and increase bandwidth. Graded-index fibers are typically used in short-haul telecommunications, LANs, and local loop applications.
Hollow-core fibers: These fibers have a hollow core, which can reduce the effects of non-linearities and enable propagation of high-power laser beams. Hollow-core fibers are typically used in high-power laser delivery and spectroscopy applications.
Highly birefringent fibers: These fibers have a large birefringence, which can be useful in polarization-maintaining applications such as fiber optic gyroscopes and polarization-sensitive sensors.
Chirally-coupled core fibers: These fibers have a unique core design that enables strong coupling between the core and cladding modes, which can be useful in sensing applications.
Overall, special fibers play an important role in a wide range of applications, from telecommunications and data transmission to sensing, spectroscopy, and medical applications. As technology continues to evolve and new applications emerge, the demand for special fibers is likely to increase, driving further innovation in fiber design and fabrication.
